Smoke detector

ABSTRACT

A smoke detector is disclosed wherein the output from a photocell produced by light deflected by smoke particles is utilized to produce a negative change in the voltage bias at the base emitter circuit of a PNP transistor to thereby generate a signal which is amplified through subsequent stages of amplification to energize a relay and alarm system. A supervisory control circuit is provided to activate the alarm upon failure of components in the smoke detector circuit. A calibration device and technique facilitates calibration and testing of the smoke detector.

United States Patent [72] Inventors Louis .I. DlCello, deceased late of San Mateo, Callt; Mrs. Louis J. DiCello, Legal Representative, 3805 Kenwood Ave., San

Mateo, Calif. [21] Appl. No. 705,887 [22] Filed. Feb. 13,1968 [45] Patented June 15, 1971 [54] SMOKE DETECTOR 2 Claims, 4 Drawing Figs.

[52] US. Cl 340/237S, 250/218, 340/214, 340/251 [51] Int. Cl. G08b 21/00 [50] Field of Search 340/218, 227, 228 S, 237, 237 S, 228.1, 228.2, 233, 234, 235, 236, 248, 214, 410, 251; ZOO/61.03; 317/12 Y, 130; 250/218; 307/315; 356/207, 208; 350/103 [56] References Cited UNITED STATES PATENTS 3,065,665 11/1962 Akhtar et a1 250/218 3,102,257 8/1963 Miller 317/124 3,255,441 6/1966 Goodwin et al.... 340/227 3,304,545 2/1967 Bell et a1 340/237 S 3,319,069 5/1967 Vassic 340/237 S 3,340,519 9/1967 Vasel 340/237 S 3,409,885 11/1968 Hall 340/233 2,720,642 10/1955 Blakely.. 340/251 X 3,003,108 10/1961 Thiele 307/315 X 3,103,599 9/1963 Henkels 307/315 X 3,290,593 12/1966 Crowdes.... 317/130 UX 3,396,387 8/1968 Grant, Jr. 340/410 3,065,665 11/1962 Akhtar et a1 356/103 X OTHER REFERENCES POPULAR MECHANICS, Fire Alarm Detects Both Smoke and Heat Sept. 1963 pg. 107

Transistor Circuits," Refus P. Turner Apr. 1, 1958 pgs. 92- 95 Primary Examiner-John W. Caldwell Assistant Examiner-Daniel Myer Attorney-Townsend and Townsend SUPERVISORY CONTROL OR 25A PATENTEUJUHISIQYI 3,585,621

FlG 1 SUPERVISORY CONTROL OR 25A INVl-YN'H )R. LOUIS J. DICELLO, DECEASED BY MRS. LOUIS J. DICELLO, REPRESENTATIVE FIG 3 BY TMJWJTM ATTORNEYS SMOKE DETECTOR This invention relates'to a new and improved smoke detector of the deflected beam type.

It is an object of the present invention to provide a new and improved smoke detector of the deflected beam type having increased sensitivity wherein a signal is generated by a negative change in voltage.

Another object of the invention is to provide a new and improved smoke detector circuit having improved reliability wherein a supervisory control circuit is provided to detect the failure of components in the smoke detector circuit and wherein a calibration device and technique is provided to facilitate calibration and testing of the smoke detector.

Other objects, and advantages of the present invention will become apparent in the following specification and accompanying drawings.

FIG. 1 is a schematic diagram of a smoke detector circuit embodying the present invention.

FIG. 2 is a schematic diagram of one form of supervisory control circuit for use with the smoke detector circuit illustrated in FIG. 1.

FIG. 3 is a schematic diagram of an alternate form of supervisory control circuit.

FIG. 4 is a diagrammatic view of the smoke chamber showing the calibration device.

In the embodiment of the present invention illustrated in the circuit diagram of FIG. 1 there is provided a photocell and lamp light source 11 in communication with a smoke chamber 12 and oriented with respect to each other so that light from the lamp 11 is normally not incident on the photocell 10. The smoke chamber 12 is normally provided with air passageways to the space monitored by the smoke detector so that the presence of smoke in the air of sufficient concentration deflects portions of the light from lamp 11 onto the photocell 10. The photocell 10 may be any suitable photoconductive device providing essentially infinite resistance when no light is incident on the device, and decreasing resistance with increasing incident light.

A low voltage source provided by battery or rectified and transformed voltage from an AC outlet is connected across a bias resistor 13 connected in the base emitter circuit of a PNP transistor 14. The bias resistor 13 is connected to the biasing voltage source in series with the photocell 10. Since the photocell is normally nonconducting the full voltage drop provided by the voltage source appears across the photocell which is connected to the negative terminal of the voltage source. With no light incident on the photocell 10, the PNP transistor 14 is normally nonconductive. As light from lamp 11 is deflected on the photocell 10, the resistance of the photocell decreases and a voltage drop appears across the resistor 13 producing a negatively changing bias voltage in the base emitter circuit of transistor 14. The PNP transistor thus becomes conducting in its collector emitter circuit. The PNP transistor starts conducting with a negative change in the bias voltage at its base thus producing a signal upon decrease in the resistance across photocell 10 and a negatively changing volt age drop across the bias resistor 13. The output of transistor 14 is amplified through two states of amplification by NPN transistors 15 and 16 generating a voltage at the output of transistor 16 sufficient to directly energize the alarm relay coil 17 closing the alarm relay switch 18 to an alarm system which may be a light, sound, or other suitable alarm. Thus, the amplified signal from the PNP transistor is used directly to energize the alarm relay coil. This provides greater sensitivity and control reliability than merely utilizing the signal from the PNP transistor to switch in a separate power source for energizing the alarm relay.

The bias resistor 13 may be a variable potentiometer for adjusting the sensitivity of the smoke detector. A resistance 20 in the collector circuit of transistor 16 provides current protection for transistors. Capacitance 21 connected in parallel across the relay coil 17 filters the pulsating DC across the relay coil when a rectified AC voltage source is used. The lamp light source 11 is connected across the low voltage source in parallel with the smoke detector circuit.

The smoke detector circuit is particularly suited for battery operation as the current drain on standby is practically nonexistent except for the lamp current requirements.

Silicon transistors are utilized throughout .to minimize variation of the circuit parameters with temperature.

The supervisory control circuit 25 for the smoke detector is illustrated in FIG. 2 where a plurality of smoke detectors are being utilized. The supervisory control circuit is comprised of a plurality of photoconductive devices 30 connected in series across a low voltage source which may be provided by battery or by rectified transformed voltage from an AC outlet. Each of the photocells 30 directly monitors the light from the lamp light source 11 in each smoke detector circuit. Thus, the light from the lamp light source 11 in each smoke detector circuit is directly incident on one of the photocells 30.

The voltage source is connected across a bias resistor 31 connected in the base emitter circuit of a PNP transistor 32. The bias resistor 31 is connected across the voltage source in series with the photocells 30. Since light is normally incident on the photocells 30, each provides low resistance in the circuit and a biasing voltage drop appears across the bias resistor 31. Since the photocells are connected to the negative terminal of the voltage source, the negative bias voltage at the base of transistor 32 maintains the transistor in a normally conducting state. The signal generated by transistor 32 is amplified by an amplifier stage provided by the NPN transistor 33 generating a voltage sufficient to energize relay coil 34 maintaining the relay switch 35 in a closed position. Capacitor 36 connected to parallel across the relay coil 34 filters pulsating DC voltage when a rectified AC voltage source is utilized. The relay switch 35 is connected to the alarm system so that the alarm is activated when the relay switch 35 is opened. If the lamp or any of the wires in the supervised smoke detector circuit fails, one or more of the photocells 30 will provide an infinite resistance across the voltage source, eliminating the negative bias at the base of PNP transistor 32. The transistor 32 will become nonconducting thus deenergizing relay coil 35 permitting the relay switch 35 to open, activating the alarm.

An alternate form of supervisory control circuit 25A is illustrated in FIG. 3 for use when only a single smoke detector circuit is to be supervised. The circuit is the same as that illustrated in FIG. 2 except the stage of amplification provided bytransistor 33 is eliminated.

The alarm for the supervisory circuit may be a light which is "On" when the supervisory circuit is operating and Off when the supervisory circuit is no longer energizing the relay switch thereby indicating a failure in the smoke detector circuit.

The smoke detector circuit is normally calibrated to generate an alarm signal if a predetermined concentration of smoke is present in the smoke chamber. Smoke detectors presently used are adjusted at the factory according to an actual standard smoke concentration in a test chamber. Because of the apparatus and cost involved in this form of calibration, the smoke detector is seldom tested or checked after leaving the factory. Users of the smoke detector have no way to make an accurate test or check. Because of the many variables involved in the smoke detector circuit such as the voltage source, lamp, photoconductive device, wiring, etc., whose parameters change in time, calibration of the smoke detector circuit is essential for maintaining proper sensitivity of the device.

According to the present invention, a novel calibration device is provided for testing and adjusting the smoke detector circuit to maintain sensitivity to a predetermined smoke concentration level. In the smoke chamber illustrated diagrammatically in FIG. 4 there is provided a light source 40 and photoconductive device 41 positioned generally at right angles to each other so that light from the source 40 is normally not incident on the photoconductive device 41. The smoke chamber is provided with passageways to the monitored space so that any present smoke particles deflect portions of the light beam from light source 40 onto the photoconductive device 41. According to the present invention, test probe 42 is provided for insertion through a passageway 43 provided in the smoke chamber 44. The test probe 42 is of sufficient length to reach into the space between the light source 40 and photoconductive device 41. The end of test probe 42 inserted in the smoke chamber 44 provides reflecting surfaces for the light from lamp 40 equivalent to a predetermined concentration level of smoke particles. The test probe 42 is provided with calibrations 45 previously determined by measuring the smoke reflective equivalence of the test probe 42 in standard smoke chambers for various depths of insertion of the test probe into the smoke chamber. Thus, for instance, the test probe 42 may be marked at a point along its length to indicate the equivalent reflective effect of 4 percent of smoke concentration for insertion of the test probe into a smoke chamber to that depth. Thus, by inserting the test probe into the space intersecting the photocell and light source to a predetermined depth, sensitivity of the smoke detector circuit may be adjusted to produce activation of the alarm at the desired percentage of smoke concentration. The test probe may be any suitable shape provided it is calibrated in a standard smoke chamber against a smoke detector circuit which has previously been calibrated against standard smoke concentrations. The test probe 42 may be provided with a keying groove complementary to a keying guide in the passageway 43 to maintain constant angular orientation of the probe in the passageway. The sensitivity of the smoke detector circuit is normally adjusted by changing the biasing or gain amplification of the circuit.

Representative values for components in the smoke detector circuit illustrated in FIG. 1 for a 6-795 volts rectified transformed DC source from an AC outlet are indicated in Table I.

TABLE I Circuit Element: Value 13 K- 500 14 2N 3702 15 2N3706 16 2N3706 1718 volt D .C 6

TABLE I Circuit Element: Value 20 -SL 18 21 mfd, 200 1 Reed rela Although only certain embodiments of the present invention have been shown and described other adaptations and modifications would be apparent without departing from the true spirit and scope of the following claims.

What is claimed is:

l. A smoke detector of the deflected beam type comprising: a smoke chamber having air passageways communicating with a space to be monitored; a light source communication with said smoke chamber; photoconductive means communicating with said smoke chamber and oriented with respect to the light source so that light from the light source is not substantially incident on said photoconductive means in the absence of smoke particles in said smoke chamber; a PNP transistor; bias resistor means connected in the base emitter circuit of said transistor; a low voltage source, said low voltage source being connected across said photoconductive means and said bias resistor in series; amplification means for amplifying the output. from said PNP transistor; alarm relay means energized by me amplified signal output from the PNP transistor comprising a relay coil connected across the amplified output from said ZTNP transistor and a switch activated by said relay coil; second photoconductive means communicating with said smoke chamber and oriented with respect to the light source so that light from the light source is normally directly incident on said photoconductive means; a second PNP transistor;

second bias resistor means connected in the base emitter circuit of the second PNP transistor; a low voltage source connected across said second photoconductive means and second bias resistor means in series; alarm means connected to the output from said second PNP transistor whereby the alarm means is activated when said second PNP transistor becomes nonconductirig.

2. A smoke detector of the deflected beam type as set forth I in claim 1 wherein is provided a test probe means adapted to be inserted in the smoke chamber in the space between the I light source and the photoconductive means, said test probe means having a reflective equivalence with respect to said I light source and photoconductive means of predetermined concentrations of smoke in said smoke chamber for specified j depths of insertion of the probe into the smoke chamber. 

2. A smoke detector of the deflected beam type as set forth in claim 1 wherein is provided a test probe means adapted to be inserted in the smoke chamber in the space between the light source and the photoconductive means, said test probe means having a reflective equivalence with respect to said light source and photoconductive means of predetermined concentrations of smoke in said smoke chamber for specified depths of insertion of the probe into the smoke chamber. 